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The article explores the in-depth residual stress evolution of a surface-rolled titanium alloy subjected to fretting fatigue. The study aims to provide data for establishing an accurate fretting fatigue life prediction model by examining the surface residual stress distribution at different stages of fretting fatigue loading. The research highlights the complex stress distribution at the fretting wear zone and the impact of fretting wear on the evolution of residual stress, emphasizing the role of contact stress and fatigue stress in this process. The study suggests practical engineering approaches to mitigate residual stress release during fretting fatigue loading, such as using lubricants and employing techniques like induction hardening for surface strengthening. [Extracted from the article]

The high‐temperature fretting fatigue damage characteristics of dovetail specimens strengthened by nanosecond laser (NL) and nanosecond combined femtosecond laser (F‐NL) were investigated. The results show that the fretting fatigue life of the NL strengthened sample (NL sample) is improved by 211.2% compared to the base metal samples (BM sample). The lifetime of the nanosecond combined femtosecond strengthened sample (F‐NL sample) was increased by 319.6%. It was attributed to the strengthening introducing hardened layers, residual compressive stress field, and high density of dislocations. The combined strengthening process reduces the surface roughness of the NL strengthened surfaces, while the strengthening influence layer is further increased. The fracture morphology shows that the crack source of the strengthened specimen has changed from multi‐source sprouting to single‐source sprouting, and the crack source sprouted on the subsurface. The fatigue strip morphology similarly confirms that a reduction in the crack propagation rate occurs. Highlights: Dovetail specimens were subjected to fretting fatigue testing at 500°C.Composite laser peening reduces surface roughness and stress concentrations.Mechanism of fatigue property enhancement after combined laser peening revealed. [ABSTRACT FROM AUTHOR]

Modern Total Hip Arthroplasty (THA) has evolved allowing orthopaedic surgeons for an exact reconstruction of hip biomechanical parameters thanks to modularity. Modular hip replacement represents, in fact, the best way to reconstruct the joint compared to conventional femoral stems. However, the modular implants are not massively used because of the high risk of breakage. One of the most common causes of their failure is the fretting corrosion at the neck-head interface combined with their relative micro-motion. Thus, the neck component undergoes major wear stresses leading to the implant failure. In order to avoid the risk of failure due to the corrosion fretting, it is necessary to improve the contact surfaces. Furthermore, available actual standards provide long testing procedure for verifying the overall modules fatigue performance thus discouraging researchers to search for possible solutions by changing the manufacturing process of the modules. This work presents a viable manufacturing technique for producing high performance neck components, proposing, at the same time, a faster and reliable testing procedure to predict the wear rate and its driving mechanism affecting the module. Thus, Ti6Al4V neck components have been manufactured by means of burnishing process at varying processing conditions which led to different surface characteristics. Different necks have been tested under real conditions for fretting fatigue simulating a walking loading cycle. Relative micromotions, together with information related to wearing path and operating conditions have been extracted online while testing, using the phase-based motion estimation method (PBME). The overall results demonstrate that burnishing process can tremendously improve the performance under service of the neck component and the proposed testing methodology is able to drastically reduce the testing time improving the reliability of the results. [ABSTRACT FROM AUTHOR]

In this paper, a modified theory of critical distance (TCD) method (i.e., Gradient‐TCD method) is proposed, which combines fatigue parameter gradient and the TCD, to estimate fretting fatigue life of dovetail joints. The advantage of Gradient‐TCD method lies in utilizing the gradient parameters to effectively characterize the local effect zone caused by fretting, thereby enabling the determination of a suitable critical distance length independent of material fatigue parameters. The reliability and predictive capability of the method is validated through experimental results. Furthermore, this method demonstrates insensitivity to mesh size, resulting in an 83.6% reduction in computational time while maintaining the predictions within the two‐times scatter band. The novel Gradient‐TCD method may provide an efficient and reliable approach for fretting fatigue life prediction, which holds promise for evaluating complex full‐scale fretting problems. Highlights: A Gradient‐TCD method was proposed to determine the length of critical distance.The Gradient‐TCD method effectively predicts the dovetail joints fretting fatigue life.Its insensitivity to mesh size results in an 83.6% reduction in computation time.It provides a promising solution for full‐scale fretting fatigue evaluation. [ABSTRACT FROM AUTHOR]

The study investigated the fretting fatigue behavior of a bridge‐flat component, utilizing a flat specimen with two bridge‐type pads tested under cyclic loading. Numerical simulations were also carried out using the finite element method. Firstly, precise calculations of contact stress were performed with the material's elastoplastic model. Secondly, the stress distribution on the maximum stress cross‐section was extracted, and the stress gradient was computed. Finally, a stress fatigue life prediction model considering the stress gradient was proposed, and the predicted life was compared with the test life. The results of the study revealed that the specimens exhibited high stress gradients at the edges of the contact region during the bridge‐flat tests. In comparison with plain fatigue, fretting fatigue life was significantly reduced. The life prediction model proposed in this paper demonstrated good accuracy for predicting fretting fatigue. Highlights: A novel stress‐fatigue life prediction model for fretting fatigue was proposed.Parameters in the new model are easy to obtain with FEM and have good physical significance.A new stress gradient and critical distance calculation method was proposed.The performance of the new model shows good accuracy. [ABSTRACT FROM AUTHOR]

In the aviation industry, structures made from high-strength titanium alloy TC21 frequently suffer from fretting fatigue (FF), resulting in shortened service life. FF is significantly influenced by the surface integrity (SI) parameters. This study aims to investigate the effect of SI parameters, including microstructure and surface roughness, on the FF properties of TC21. It is implemented by introducing the crystal plasticity finite element method (CPFEM). The CPFEM parameters of single grain of α-Ti in TC21 were obtained by fitting the experimental and simulation data of nanoindentation test. On this basis, the FF of TC21 is studied by means of multiscale modeling method, which couples a global model with a CPFEM sub-model composed of hierarchical microstructure. In the global model, surface roughness was considered. While in the CPFEM sub-model, microstructure was incorporated as well. The FF sub-model shows that the stress was unevenly distributed due to the inconsistency in mechanical behavior of TC21. Both the maximum von Mises stress and the maximum Fatemi-Socie (FS) parameter occurred at the grain boundaries in the subsurface layer. The prismatic slip system (1‾010)[1‾21‾0] is highly sensitive to FF. For the orientation of ∥X-axis, the lowest FS value of 1.137 × e−2 was obtained at the surface roughness of 0.8 μm, meaning the smallest damage. While the orientation of ∥X-axis and random orientation are most sensitive to FF, their FS values reaching 2.019 × e−2 and 2.090 × e−2, respectively.

High-strength titanium alloy TC21 is often used to make aircraft load-bearing components in the aviation field. However, due to vibration, load-bearing components often suffer from fretting fatigue (FF), which greatly reduces their actual service life. Nowadays, laser shock peening (LSP) is being recognized as an effective strengthening process for many materials. Therefore, in this study, the effectiveness of LSP on the strengthening of high-strength titanium alloy TC21 is studied, in terms of surface integrity and FF properties. TC21 fretting specimens and tests are designed. Before fretting tests, the specimens are processed by LSP with varying laser pulse energies, number of shocks and overlap rate, and their surface integrity and FF properties are analyzed. It is found that the greater the laser pulse energy and number of shocks, the higher the surface hardness and compressive residual stress, the more the grain refinement, the greater the improvement in FF life. Under 32J-50%-T1, the FF life is improved by 191.3% compared with BM. But the overlap rate has little effect on surface integrity and FF life. Meanwhile, there forms amorphous structures, which tended to be transformed into nanograins during fretting process. This transformation is helpful for prolonging FF life due to its action of energy absorption. This study reveals the strengthening mechanism of LSP on TC21 and its effect on the FF properties of TC21 specimens.

The turbine blades of aero-engines are subjected to cyclic high-low cycle loads in actual service environments，which is a typical high-low cycle micro motion fatigue condition. The frequent occurrence of fatigue fracture in turbine blades due to fretting fatigue seriously affects the safe operation of aero-engines. In order to study the high-low cycle fretting fatigue problems of hot end component materials，this paper designs an Inconel718 tenon connection simulation component and conducts high-low cycle composite fretting fatigue tests on it. Three different load/frequency experiment conditions were designed to compare the life distribution of the simulated parts under different conditions. The results show that high/low cycle load has significant influence on fretting fatigue life. With the increase of high/low cycle load or frequency，the fretting fatigue life of joints decreases. The test results have proven that the high-low cycle fretting fatigue test of the tenon joint structure effectively reproduces the actual service condition of turbine blades. By displaying the explicit finite element analysis，the predicted crack initiation location shows less dispersion compared to the experimental results.

Fretting fatigue is a common engineering failure phenomenon, often resulting in a shorter lifespan compared to plain fatigue. To consider the interaction between different scales, this study proposes a fully coupled two‐scale model based on continuum damage mechanics (CDM) and the crystal plastic finite element method (CPFEM) for the fretting fatigue crack initiation. Furthermore, the life data series are generated by employing feature engineering and long short‐term memory (LSTM) networks optimized with a genetic algorithm, ensuring the minimization of redundancy. Additionally, the genetic algorithm, enhanced by the Markov chain Monte Carlo method, was used to optimize the hyperparameters of the LSTM network. Simulation results indicate that the two‐scale model offers improved accuracy in predicting crack initiation life and provides physical information of crack initiation from different scales simultaneously. [ABSTRACT FROM AUTHOR]

This paper evaluates the capability of the theory of critical distances (TCD) coupled with the Fatemi–Socie (FS), Smith–Watson–Topper (SWT), and normal stress range (S‐N) criteria for the lifetime estimation of combined fretting fatigue, that is, the combination of bending and axial loading modes, for 316L stainless steel along with the effect of increasing the grain size of the material. After evaluating the stress field, the point, line, area, and volume methods have been implemented to estimate the lifetimes of fretting fatigue experiments based on the dependency of the critical distance on the number of cycles to failure. Whereas the area and volume methods were overestimating the lifetimes, the point and line methods were more accurate. FS and SWT criteria were proper in lifetime estimation, but the normal stress range (S‐N) criterion was not a safe criterion. At the same time, increasing the grain size of the material leads the TCD to be more conservative. [ABSTRACT FROM AUTHOR]

This study investigates the surface changes and fretting phenomena at neck-head interface of Ti6Al4V alloy. In particular, hip necks subjected to burnishing process are the objective of the experimental campaign. Ti6Al4V is a widely used material in orthopedic implants due to its excellent biocompatibility and mechanical properties. However, the potential for fretting fatigue is a common concern in hip implants requiring the exploitation of surface modification techniques to enhance the implant's performance and durability. Burnishing process involves the controlled application of mechanical pressure to the implant's surface, which can generate residual stresses and changes in surface topography. By employing advanced surface characterization techniques, including micrograph and profilometry, the surface modifications induced by burnishing were evaluated. Furthermore, fretting fatigue assessment was carried out through mechanical testing, simulating the conditions encountered in the hip joint during typical daily activities. Finally, an emerging sensing technology in the field of non-destructing optical testing, phase-based motion estimation (PBME) was employed in order to assess the surface gradual degradation before failure. [ABSTRACT FROM AUTHOR]

Shafts with a stepped shoulder are particularly well known in the field of drive technology. In combination with a form-fit shaft–hub connection, the shaft shoulder fixes the hub on the shaft as well as being responsible for the absorption of the axial forces. With profiled shafts, there is a notch overlay in the shaft shoulder, involving the shaft shoulder and profile. If the hub is also connected with the profiled shaft, the hub edge acts as an additional notch in the shaft shoulder area. The multiple resulting notches have not previously been part of research activities in the field of innovative trochoidal profile connections. Compared to conventional positive-locking connections, such as the keyway connection or the involute splined shaft profile, the favourable features of trochoidal profiles have only been based on connections with stepless shafts without a shoulder in previous studies. Accordingly, this article addresses numerical and experimental investigations of trochoidal profile connections with offset shafts for pure torsional loading. Focusing on a hybrid trochoid with four eccentricities and six drivers, a well-founded numerical and experimental investigation was carried out with numerous fatigue tests. In addition, the influence of a shaft shoulder was also demonstrated on simple epitrochoidal and hypotrochoidal profiles.

The mixed-mode loading fretting fatigue caused by the complex geometry of components and combinations of boundary conditions is a common failure mechanism in engineering components, which can dramatically reduce fatigue life. In this paper, a cylinder-on-flat numerical model was established to investigate tension–bending mixed-mode fretting fatigue. The finite element method in conjunction with two criteria, plane parameters McDiarmid (MD) and Smith–Watson–Topper (SWT), were used to evaluate the effects of mode angle, oblique loading, and stiffness ratio on the contact width, the maximum equivalent stress of the specimen, the surface stress, the fretting damage initiation location, and the extent of the damage initiation. The results indicate that the extent of fretting damage increases with the mode angle, and the characterization parameters are sensitive to smaller mode angles. The contact width, peak surface stress, maximum damage parameters, and damage initiation location can be effectively adjusted by the stiffness ratio. The findings may provide insights into fretting fatigue behavior under complex loading conditions, potentially contributing to enhanced structural safety and reliability for tension–bending mixed-mode loading. [ABSTRACT FROM AUTHOR]

Shafts with a stepped shoulder are particularly well known in the field of drive technology. In combination with a form-fit shaft–hub connection, the shaft shoulder fixes the hub on the shaft as well as being responsible for the absorption of the axial forces. With profiled shafts, there is a notch overlay in the shaft shoulder, involving the shaft shoulder and profile. If the hub is also connected with the profiled shaft, the hub edge acts as an additional notch in the shaft shoulder area. The multiple resulting notches have not previously been part of research activities in the field of innovative trochoidal profile connections. Compared to conventional positive-locking connections, such as the keyway connection or the involute splined shaft profile, the favourable features of trochoidal profiles have only been based on connections with stepless shafts without a shoulder in previous studies. Accordingly, this article addresses numerical and experimental investigations of trochoidal profile connections with offset shafts for pure torsional loading. Focusing on a hybrid trochoid with four eccentricities and six drivers, a well-founded numerical and experimental investigation was carried out with numerous fatigue tests. In addition, the influence of a shaft shoulder was also demonstrated on simple epitrochoidal and hypotrochoidal profiles. [ABSTRACT FROM AUTHOR]

Saddle systems are a popular solution for supporting cables in cable-stayed bridges. Fretting fatigue failure of cables at saddle supports is a primary design consideration for these systems. Critical parameters that affect the fretting fatigue life of the cables are the contact forces and the slip displacements at the contact points between the cables and the saddle. Determining these critical parameters is the first step in evaluating the fretting fatigue life of the cables. Wear in the contact points between the cables and the saddle can affect the load distribution in saddle systems and consequently affect these critical parameters. However, the effect of wear has not been studied in the previous works. This paper first discusses the methods proposed in the literature for evaluating contact forces and slip displacements in the contact points between a cable and a saddle. Then, a finite element model of the problem and a framework for modelling the wear are presented. Finally, fretting fatigue life is determined based on the different studied approaches. The main highlights of the current study are considering the effect of wear in the simulation and employing an enhanced FE model for slip displacement calculations. The results of the basic model without wear effects showed that the first contact point between the cable and the saddle is critical for fatigue failure. However, by incorporating wear in the model, the contact force at the first point dropped and the second contact point became critical; this is in line with the observations in large-scale fatigue tests of saddle systems. [ABSTRACT FROM AUTHOR]

Fretting fatigue contributes significantly to the fatigue failure process in steel wire ropes at the wire‐to‐wire trellis contact region with partial slip conditions. In this respect, this work demonstrates a new damage‐based fretting fatigue model for the prediction of such a failure process. The model is based on Lemaitre's damage equations for quasi‐brittle material with a damageable micro‐inclusion embedded in an elastic meso‐element. It incorporates the cyclic degradation of the elastic modulus of the drawn steel wire material. The fatigue life model acknowledges the mean stress effect. The constitutive and damage equations are formulated into user material (UMAT) subroutine for integration with Abaqus finite element analysis code. The localized fretting fatigue damage mechanism is simulated with an isolated two‐wire model. The effect of the contact condition with the coefficient of friction of 0.2 and 0.8 on the contact mechanics of the drawn wires is considered. The fretting fatigue mechanism map is established for each simulation case. The simulated results of N0 (no of cycles to initiate damage) and damage variable, D, confirm the fretting fatigue condition as the damage occurs in the slip region of the contact area for both the frictional conditions. The results were found in agreement with the previously establish Ruiz fretting parameter. This study will provide a base for the onward reliability assessment of steel wire ropes. Highlights: A damage‐based Lemaitre two‐scale model has been modified for the fretting fatigue mechanism in the steel wire ropes.A unified curve of residual elastic modulus has been established through interrupted fatigue tests for different load ratios.A UMAT Subroutine is developed using ABAQUS software. The response of the damage model has been investigated using different parameters like Damage D, Residual Elastic Modulus E(N), Number of cycles to initiate damage N0, and von Mises stress at the contact region. [ABSTRACT FROM AUTHOR]

To reasonably forecast the crack initiation characteristics of fretting fatigue, this study evaluates the accuracy of several damage models. The existing experimental and simulation investigations are compared, noting the similarities and differences in the crack initiation location, crack orientation angle, and crack initiation life predicted by various damage models. It is crucial to employ a reasonable and reasonable damage prediction model of fretting crack initiation life, as fretting fatigue, a phenomenon of mechanically fastened connecting parts, can considerably reduce the fretting fatigue life of the components. This paper compares the fatigue damage prediction models of fretting fatigue specimens under partial slip conditions, and it will help researchers understand the benefits and drawbacks of various damage models and give them the knowledge and foundation to select the more reasonable fretting fatigue damage model. Highlights: A structured meshing technique and coupled constraint loading strategy are proposed.The cyclic characteristics of fretting contact parameters are analyzed.A normalized parameter for comparing the fatigue damage models is proposed.The accuracy of the different fretting fatigue damage models are compared. [ABSTRACT FROM AUTHOR]

Fretting damage on contacting surfaces introduces major challenges in mechanical assemblies. Thermal sprayed hardmetal coatings are extensively used for surface modification in tribological applications under demanding conditions and may also be subjected to fretting-inducing loading. In the present work, the fretting behavior of High Velocity Oxy-Fuel (HVOF) and High Velocity Air–Fuel (HVAF) sprayed WC-10Co-4Cr coatings against quenched and tempered (QT) steel was studied by using a single bolt joint-type fretting experiment. This experimental approach was selected to obtain realistic data on the fretting fatigue performance of the contact pairs (both coating-to-steel and coating-to-coating). Experimental results were completed with continuum-scale linear elastic finite element method (FEM) calculations. [ABSTRACT FROM AUTHOR]

Fretting fatigue is a specific fatigue phenomenon. Due to the complex mechanisms and multitude of influencing factors, it is still hard to predict fretting fatigue life accurately, despite there being many works on this topic. This paper developed a particle-swarm-optimized back propagation neural network to predict the fretting fatigue life of aluminum alloys using the test data gathered from the published literature. A commonly used critical plane model, the Smith, Watson, and Topper criterion, was used as a contrast. The analysis result shows that the proposed fretting fatigue life prediction neural network model achieves a higher prediction accuracy compared to the traditional SWT model. Experimental validation demonstrates the effectiveness of the model in improving the accuracy of fretting fatigue life prediction. This research provides a new data-driven methodology for fretting fatigue life prediction. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of duplex plasma nitriding and diamond-like carbon (DLC) coatings on the pure fatigue and fretting fatigue properties of 16MnCr5 steel extracted from industrial piston pins used in combustion engines. Two different nitriding and DLC coating processes were performed: ''DLC-A'' and ''DLC-B''. The Raman spectrometry and microhardness tests were utilized to evaluate the formation of DLC coating on the sample. Subsequently, the pure and fretting fatigue tests (at 350 MPa and under 100 Hz of the frequency) were performed on as-cast and DLC-coated specimens to obtain the effect of coatings on the fatigue behaviors of the 16MnCr5 steel. Finally, the formation of the DLC layer and the fracture mechanisms were also briefly investigated using field-emission scanning electron microscopy. Then, the obtained results demonstrated that DLC coating (''DLC-B'') increased the fatigue lifetime of 16MnCr5 steel by 47.7 % and 85.3 % in pure and fretting fatigue conditions, respectively. This layer can improve the surface properties of engineering materials and components, which can enhance the fatigue lifetime by increasing microhardness and compressive residual stress, reducing wear and friction, and improving adhesion between the substrate and coating. However, due to the white layer, the “DLC-A” improperly enhanced the material performance.

In this paper, combined experimental and numerical methods are applied to investigate the effect of different contact stress and slip amplitude on the fretting fatigue (FF) behaviour of TC11 titanium alloy with gradient nanostructure introduced by ultrasonic surface rolling process (USRP). The properties of gradient nanostructure are characterized using scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray residual stress tester, microhardness tester. As evidenced by the FF experimental results, USRP can significantly improve the FF life of TC11 by introducing large compressive residual stress and work hardening layer. The dominant parameters in improving the FF resistance under different loading conditions are investigated. In addition, the simulated results from Abaqus show that contact stress plays a more important role in influencing FF life compared to fretting bridge span, which is attributed to the change in slip amplitude and stress concentration. Fretting fatigue life initially increases and then decreases with contact stress and there is a contact stress threshold that leads to minimum lifetime. This threshold of USRP specimens is greater than that of untreated specimens. The transition of fretting mode along with contact stress is observed and discussed.

Recently, a new dissimilar mechanical joining method, dimple spot welding (DSW), has been developed for joining steel sheets and aluminum alloys. In this study, tensile shear tests and fatigue tests were conducted on four types of dissimilar lap joints, with two types of steel sheets and two types of Al alloys joined by DSW. Both the tensile shear strength and fatigue strength of DSW joints were found equal to or greater than those of a self‐piercing riveting (SPR) joint. In all four types of DSW joints, fatigue cracks were initiated from the Al alloy and were associated with fretting induced by repeated contact and friction. A finite element analysis showed that the tangential stress was mainly governed by the friction coefficient and also affected by the steel sheet strength. Higher‐strength steel led to lower tangential stress, resulting in a longer fatigue life for the DSW joint. Highlights: A dimple spot welding (DSW) is developed for joining steel sheets and aluminum alloys.Tensile shear tests and fatigue tests are conducted on DSW joints and SPR joint.DSW joints shows greater tensile shear strength and longer fatigue lives than SPR joint.Fatigue cracks in DSW joints were initiated associated with fretting. [ABSTRACT FROM AUTHOR]

This paper evaluates the influence of contact pressure on the surface contact state, fretting damage degradation mechanism, crack initiation and propagation characteristics, and fretting fatigue life of A319‐T6 cast aluminum alloy in fretting fatigue test using bridge‐type fretting pad. For a certain range of contact pressure, the fretting fatigue life exhibits a trend of increasing and subsequently decreasing with increasing contact pressure. With finite element analysis, the fretting contact region can be divided into two characteristic zones according to the dynamic evolution of the contact status within one fatigue cycle. The contact pressure affects both the distribution of the two characteristic zones as well as the relative slip range, which results in distinct fretting damage mechanisms. The nucleation characteristics and propagation paths of fatigue cracks under three typical contact pressures were analyzed considering the effects of fretting damage and heterogeneous microstructures of the alloy, accounting for the contact pressure dependency of the fretting fatigue life. Highlights: The dynamic evolution of the contact status affected by contact pressure is considered.The fretting damage evolution with the variation of contact pressure is evaluated.The nucleation characteristics and propagation paths of fatigue cracks are elaborated.The contact pressure dependency of the fretting fatigue life is summarized. [ABSTRACT FROM AUTHOR]

Railway axles are safety-critical components of the rolling stock and the consequences of possible in-service failures can have dramatic effects. Although this element is traditionally designed against such failures, the initiation and propagation of service cracks are still occasionally observed, requiring an effective application of non-destructive testing and structural health monitoring approaches. This paper investigates the application of structural health monitoring by acoustic emission to the case of solid railway axles subject to fretting fatigue damage. A full-scale test was performed on a specimen in which artificial notches were suitably manufactured in order to cause the initiation and evolution of fretting fatigue damage up to the stage of relevant propagating fatigue cracks. During the test, both periodical phased array ultrasonic inspections and continuous acquisition of acoustic emission data have been carried out. Moreover, at the end of the test, the specimen was inspected, analyzed and evaluated by visual inspection and magnetic particles testing, while acoustic emission raw data were post-processed by a special unsupervised machine learning algorithm based on an Artificial Neural Network. It is demonstrated that the proposed methodology is very effective to detect the onset of crack initiation in a non-invasive and safe way. [ABSTRACT FROM AUTHOR]

A study was conducted to compare the pure fatigue and fretting fatigue properties of AM60 magnesium alloys, with and without 3D-printed PLA coatings. The PLA coating layers led to an increase in the fatigue lifetime in both pure and fretting conditions. They delayed the crack initiation time compared to uncoated samples, thereby increasing fatigue lifetime. Additionally, in the case of fretting fatigue, PLA coating caused the fretting pads to reach the magnesium alloy later, which also contributed to the longer lifetime of coated samples, compared to uncoated specimens. Using field emission scanning electron microscopy, all specimens exhibited the brittle fracture behavior, with the presence of both cleavage and quasi-cleavage marks. By the fractography, it was found that the number of cracks in coated samples decreased in both pure and fretting fatigue conditions. Remarkably, PLA coating during fretting fatigue resulted in a significant enhancement of the fretting fatigue lifetime, within 56%–2182 %.

The mixed-mode loading fretting fatigue caused by the complex geometry of components and combinations of boundary conditions is a common failure mechanism in engineering components, which can dramatically reduce fatigue life. In this paper, a cylinder-on-flat numerical model was established to investigate tension–bending mixed-mode fretting fatigue. The finite element method in conjunction with two criteria, plane parameters McDiarmid (MD) and Smith–Watson–Topper (SWT), were used to evaluate the effects of mode angle, oblique loading, and stiffness ratio on the contact width, the maximum equivalent stress of the specimen, the surface stress, the fretting damage initiation location, and the extent of the damage initiation. The results indicate that the extent of fretting damage increases with the mode angle, and the characterization parameters are sensitive to smaller mode angles. The contact width, peak surface stress, maximum damage parameters, and damage initiation location can be effectively adjusted by the stiffness ratio. The findings may provide insights into fretting fatigue behavior under complex loading conditions, potentially contributing to enhanced structural safety and reliability for tension–bending mixed-mode loading.

Cantilever fans exhibit the desirable properties of low noise and long lifetime. However, current cantilever fan designs have low volumetric flow rates compared to other fan types. The study was focused on improving the volumetric flow rate, while keeping its desirable properties. Here we show a cantilever fan system that achieves a volumetric flow rate of 58.9 L/s. This was achieved by increasing the size of the fan blades, using high strength spring steel fan blades at their endurance limit, driving the fans with a custom linear motor and suppressing edge vortexes with shrouding. The flow rate reported here is 118 times higher than has been previously reported.

Saddle systems are a popular method for supporting the cables at the pylons of cable‐stayed bridges. Fretting fatigue failure of bridge stay cables is a major design consideration for saddle systems. Current design provisions require large‐scale tests of these anchoring systems. However, such tests are costly and time‐consuming. With this in mind, the current paper presents a small‐scale fretting fatigue setup to evaluate the fretting fatigue behavior of bridge stay cable wires at saddle supports. In this paper, fretting tests are conducted on bare and galvanized wires. Hourglass samples are then used to evaluate the material properties and plain fatigue performance of the studied wires. Finally, the microstructure of the wires is evaluated, and the influence of defects on the fretting fatigue life of the wires is discussed. Highlights: A small‐scale fretting fatigue test setup for bridge stay cable wires is designed.Fatigue and fretting fatigue performance of bare and galvanized wires are evaluated.The microstructure and properties of two typical bridge cable wires are explored.The effects of defects on fatigue and fretting fatigue life of wires are discussed. [ABSTRACT FROM AUTHOR]

Fretting fatigue is a well-known and dangerous damage mode that occurs on the mating surfaces of mechanical components, mainly promoted by a combination of stress distribution, contact pressure distribution, and relative sliding (micro)motion between the surfaces. However, predicting this mechanism is challenging, necessitating specific studies for each assembly due to variable influences. This article presents a methodology for evaluating fretting fatigue damage at the contact between a titanium connecting rod big end and the bearing, adopting the Ruiz parameter as a quantifying damage index. For this purpose, a thermal-structural finite element model is prepared. In particular, the machining and assembly of the split conrod big end are simulated, considering thermal effects. A full engine cycle is first simulated, and results are used for identifying critical instants to be considered for accurate yet computationally efficient calculations. The dependence of fretting fatigue on three factors is studied: bearing crush, bolts tightening torque, and friction coefficient between the big end and the bearing. In summary, the damage increases with a higher crush and friction, while tightening torque has marginal effects. Following a 20% increase in crush height, a corresponding 10% rise in the Ruiz parameter is observed. Conversely, reducing the crush height by 20% leads to an approximately 8% decrease in the Ruiz parameter. When the influence of the bolt preload is taken into account, only a marginal 1% increase of the Ruiz parameter is recorded despite a 30% rise in preload. Evaluating the impact of the friction coefficient on the Ruiz parameter reveals an almost linear relationship. These findings suggest that adjusting the screw preload can enhance the hydrodynamic behavior of the bearing without exacerbating fretting. Furthermore, exploiting the linear correlation between Ruiz and the friction coefficient allows for the generalization of results obtained with specific coefficient values. This methodology can, therefore, serve as a valuable reference for adjusting different variables during the initial design phases of a four-stroke internal combustion engine's dismountable connecting rod. [ABSTRACT FROM AUTHOR]

The appearance of fretting fatigue cracks in bolted sheets limits their lifetime. Furthermore, repairing these failures requires much effort due to needing to replace the components instead of replacing just the bolt. To prevent such failures, the purpose of this study is to understand the failure mechanism and to identify the major influencing parameters. Therefore, a representative joint of a bolt of size M22 and sheet material were investigated by experiments and a finite element analysis. The experiments were conducted over a wide range of preloads from zero to maximum preload. It turned out that the failure mode changes at 50 kN. For this preload, the influence of the surface and the use of a lubricant was observed. A grinded surface as well as the use of lubricant showed a change in the failure mode. The accompanying simulation showed that an analysis of the stresses delivers no proper explanation for the observed effects in the experiment. Therefore, the contact status was analyzed for various preloads and friction coefficients. The results correlate with the change in the failure mode. The conclusion is that both the stress state and the tribological behavior influence the failure mode and have to be considered in a numerical analysis. [ABSTRACT FROM AUTHOR]

In this paper, a numerical model of fretting fatigue analysis of cable wire and the fretting fatigue damage constitutive model considering the multi-axis effect were established, and the user material subroutine UMAT was written. Then, the constitutive model of wear morphology evolution of cable wire and the constitutive model of pitting evolution considering the mechanical-electrochemical effect were established, respectively. The corresponding subroutines UMESHMOTION_Wear and UMESHMOTION_Wear_Corrosion were written, and the fretting fatigue life was further predicted. The results show that the numerical simulation life obtained by the program in this paper has the same trend as the tested one; the error is only about 0.7% in the medium life area; When the normal contact force increases from 120 to 240 N, the fretting life of cable wire decreases by 25%; When the evolution of wear morphology and corrosion effect are considered simultaneously, the depth of the wear zone exceeds 0.08mm after 600,000 loads, which is much larger than 0.04mmwhen only the evolution of wear morphology is considered. When the evolution of wear morphology and corrosion morphology is considered simultaneously, the damage covers the whole contact surface after 300,000 loads, and the penetrating damage zone forms after 450,000 loads, which is obviously faster than that when only the wear morphology evolution is considered. The method proposed in this paper can provide a feasible numerical simulation scheme for the visualization of the damage process and accurate life prediction of cable-supported bridges. [ABSTRACT FROM AUTHOR]

Physicomechanical characteristics of 15Kh16k5N2MVFAB-Sh steel (0.15C–16Cr–5Co–2Ni–0.7V–0.6Mo–0.3Nb–0.4N): wear resistance at 20°C and 500°C and resistance to fretting fatigue at 20°C without and with coatings obtained by the method of vacuum-arc deposition using targets based on the MAX phases of Ti 2 AlC and (Ti 1 - x Nb x) 2 AlC , where x = 0.1 and 0.2, are investigated. At 20°C the friction coefficient and the wear specific rate of all coatings are greater than that of the studied steel in contact with a ShKh15 steel (1.0C–1.5Cr–0.3Ni–0.3Mn–0.3Si–0.25Cu) ball under a load of 2 N. Unambiguous relationship between microhardness and tribological characteristics of materials has not been recorded. The resistance to fretting fatigue of the samples with Ti 2 AlC -based coating in contact with the Ni-alloy (17Cr–12W–11Fe–6Co–3Ti–1.5Nb–1.6Al) in high-cycle region (N > 10 5 cycles) is significantly higher than that of uncoated samples. The tribological characteristics of all materials decrease at 500°C but the least for samples with Ti 2 AlC based coating. We have not found positive influence of niobium doping on the wear and fretting fatigue resistance of these coatings. [ABSTRACT FROM AUTHOR]

In this study, a new model is developed for fretting fatigue crack initiation life prediction based on the slip amplitude as a macroscopic feature of the contact interfaces. The main difference between the presented model and many other fretting fatigue life prediction models is the focus on the fretting specific characteristics. In this model, a damage parameter is combined with a damage severity factor to obtain a new fretting fatigue crack initiation life prediction parameter. To investigate the accuracy of this new parameter, a series of fretting fatigue tests were conducted. Also, crack initiation life data from the literature were added to enhance parameter accuracy investigation. It was shown that the effective slip amplitude was an unbiased geometric-independent parameter in fretting fatigue crack initiation life prediction. Also, comparison of the prediction results from the effective slip amplitude with those of Smith-Watson-Topper and Ruiz parameters illustrated that the new parameter could outperform available fretting fatigue life prediction parameters. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mechanical Strength / Jixie Qiangdu is the property of Zhengzhou Research Institute of Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The influence of duplex surface treatment including a Cr/CrN nanolayered coating deposited by cathodic arc physical vapor deposition (CAPVD) and an alumina layer coated by hard-anodizing method on the fretting fatigue strength of Al7075-T6 alloy is studied in this investigation. Although fretting fatigue life of both single Cr/CrN coated alloy and Cr/CrN coating deposition onto hard-anodized alloy was increased in high cycle fatigue (HCF) regime, employing an alumina layer as a pretreatment for the Cr/CrN deposition enhanced the life improvement in the HCF regime. In low cycle fatigue (LCF) regime, despite a decrease in fretting fatigue life of both Al7075-T6-coated alloys, using the alumina layer beneath the Cr/CrN coating resulted in mitigation of fretting fatigue life deterioration. Interestingly, a single-hard-anodized specimen represented a completely different variation trend of fretting fatigue life in HCF and LCF regimes. Unlike the as-received and single-hard-anodized specimens, Cr/CrN-coated specimens did not bear the maximum axial stress, 260 MPa. Partial slip regime was mostly seen at the contacting area. [ABSTRACT FROM AUTHOR]

Fretting fatigue failure of 2024 aluminum alloy under alternating normal load was investigated. A biaxial fretting fatigue test system is designed which can apply alternating phase load and distal load. Through Abaqus finite element analysis, the normal loading device of the test bench was analyzed and calculated, and the influence of the force conduction error and the swing angle of the fretting pad on the test accuracy was investigated, the accuracy of loading test machine is verified. The influence of phase difference of 0°, 45° and 90° on fatigue life of 2024 aluminum alloy under alternating normal load was studied. The test results show that the life of 2024 aluminum alloy specimens increases with the increase of phase difference. Through the analysis of wear state, it is found that the influence of wear is small when the phase difference is 0° and 45°, and the life increases with the increase of phase difference. When the phase difference is 90°, the wear is more serious. Under the joint action of wear and fatigue damage, the fatigue life of specimens at 90° phase difference is further increased. The overall trend of fretting fatigue life of specimens under alternating normal load is that the life increases with the increase of phase difference, and the wear increases with the increase of phase difference.

The present study posits that variations in maximum shear strain energy are the principal determinants for the onset of fretting fatigue cracks. We propose a refined critical plane methodology, termed the shear stress-strain interaction (SSI) critical plane method, predicated on shear strain, for predicting fretting fatigue crack initiation characteristics. The novelty of this methodology resides in its focus on cyclic shear strain as the genesis of crack initiation. To verify the effectiveness of the SSI critical plane method, finite element analyses using ANSYS were executed on fretting bridge and pad models to quantify the SSI interaction parameters. A comprehensive evaluation against established metrics-maximum shear range, stress-weighted tangential parameters, and fretting parameters was undertaken. The findings, in alignment with extant experimental data, confirm the robustness of the proposed method.

The fatigue failure mechanism of bending fretting for cyclic softening material 6061-T6 aluminum alloy was researched by experiment and finite element method. The influence of cyclic load on bending fretting fatigue was researched and the damage characteristics under different cycles was discussed experimentally though SEM images. In the simulation, a normal load transformation method was employed to obtain a simplified two-dimensional model used for simulating the bending fretting fatigue from a three-dimensional model. An advanced constitutive equation with the Abdel–Ohno rule and isotropic hardening evolution was transplanted into ABAQUS by UMAT subroutine to consider the ratchetting behavior and cyclic softening characteristics. The peak stain distributions under various cyclic loads were discussed. Additionally, the bending fretting fatigue lives and crack initiation locations referring to a critical volume method were estimated using the Smith–Watson–Topper critical plane approach and reasonable results were obtained. [ABSTRACT FROM AUTHOR]

In turbine tenon joint structures, fretting fatigue is common and can have detrimental effects on the components. To increase the fretting fatigue life, the design of tenon joint structures must be optimized. A parametric model of the three-tooth mortise and tenon joint structure is developed in this research. Sensitivity analysis yields the primary characteristic parameters, which are then employed as design variables. The objective function is the life of fretting fatigue. An aero-engine turbine three-tooth mortise and tenon joint structure was optimized against fretting fatigue using a Multi-Island Genetic Algorithm (MIGA), which was then experimentally verified. The optimization was based on the multidisciplinary optimization platform ISIGHT to write batch files integrating ANSYS and MATLAB. According to the findings, the three-tooth mortise and tenon joint structure's fretting fatigue life can be increased by 51.3% by applying the MIGA. The contact pressure was reduced by 0.54% and the maximum slip amplitude has been reduced by 13%. The approach of optimization's efficacy was confirmed. [ABSTRACT FROM AUTHOR]

Micro relative sliding exists on the contact surface of the main primary equipment's surface structures, resulting in serious fretting fatigue. The plastic effect causes serious fatigue to the structure under alternating loads. Existing fatigue life prediction models fail to fully consider the shortcomings of fretting and plastic effects, which causes the prediction results to be significantly different to real-lifeworld in engineering situations. Therefore, it is urgent to establish a fretting damage fatigue life prediction model of contact structures which considers plastic effects. In this study, a plastic fretting fatigue life prediction model was established according to the standard structural contact theory. The location of dangerous points was evaluated according to a finite element simulation. The cyclic load maximum stress value was compared with the fretting fatigue test data to confirm the error value, and the error between the proposed fretting fatigue life model and the test value was within 15%. Concurrently, we combined this with mass data analysis and research, as it is known that the contact zone parameters have an impact on fretting fatigue and affect the structural lifespan. With the help of ABAQUS, the fretting numerical calculation of the dovetail tenon model was carried out to analyze the sensitive factors affecting the fretting fatigue life of the dovetail tenon structure. By keeping the fretting load unchanged, the contact area parameters such as contact surface form, contact area width and friction coefficient were changed in order to calculate the fretting stress value, σfretting and the dovetail structure was improved to extend its fretting fatigue life. Finally, it was concluded that fretting fatigue was most sensitive to the width and contact form of the contact area. In actual engineering design, multiple factors should be considered comprehensively to determine a more accurate and suitable width and form of the contact area. For the selection of friction coefficient, on the premise of saving costs and meeting the structural strength requirements, the friction coefficient should be as small as possible, and the problem can also be solved through lubrication during processing. [ABSTRACT FROM AUTHOR]

Fretting fatigue is a specific fatigue phenomenon. Due to the complex mechanisms and multitude of influencing factors, it is still hard to predict fretting fatigue life accurately, despite there being many works on this topic. This paper developed a particle-swarm-optimized back propagation neural network to predict the fretting fatigue life of aluminum alloys using the test data gathered from the published literature. A commonly used critical plane model, the Smith, Watson, and Topper criterion, was used as a contrast. The analysis result shows that the proposed fretting fatigue life prediction neural network model achieves a higher prediction accuracy compared to the traditional SWT model. Experimental validation demonstrates the effectiveness of the model in improving the accuracy of fretting fatigue life prediction. This research provides a new data-driven methodology for fretting fatigue life prediction.

The presence of cyclic loading alongside the wear increases the probability of fretting fatigue phenomenon in the cylinder head of automobiles. In the current study, the nano-reinforcing and the T6 heat-treating impact on the fretting fatigue behavior of the cylinder head aluminum alloy were studied. Fretting fatigue tests were performed in the high-cycle fatigue regime, under 15 N contact load and four different stress levels (75, 100, 125, and 150 MPa). According to the test results, the fretting fatigue lifetime of heat-treated nano-composites under the lowest stress level increased by about 621%. Furthermore, the fracture surface of the studied aluminum alloys, the worn surface of the cast-iron ring used as fretting pads, and the derbies obtained during the fretting test were investigated with the help of field emission scanning electron microscopy. The failure behavior of the cylinder head materials concerning the presence of the quasi-cleavage and cleavage marks were brittle in all cases. In addition, as it is observed the wear mechanism of fretting pads was adhesive.

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The problem of elastic indentation by a punch having the form of a flat front face but with edge rounding, and subject to both a normal load and moment, indenting an elastically similar half-plane is considered. Contact pressure in the neighbourhood of the edges shows a local peak, and the object of the paper is to show how different combinations of normal load and moment can give rise to the same near edge behaviour and peak pressure. The result found is very simple, and of direct practical application in fretting fatigue studies, both analytical and experimental. [ABSTRACT FROM AUTHOR]